Thin wire/thick wire lead assembly for electrolytic capacitor

ABSTRACT

A capacitor containing a solid electrolytic capacitor element including a sintered porous anode body, a first anode lead, and a second anode lead is provided. The first anode lead has a thickness that is larger than a thickness of the second anode lead. A portion of the first anode lead is embedded in the porous anode body, and a second portion of the first anode lead extends from a surface thereof in a longitudinal direction. Meanwhile, the second anode lead is electrically connected to the anode body for connection to an anode termination. In one embodiment, the second anode lead can be directly connected to a surface of the anode body. In another embodiment, the second anode lead can be indirectly connected to the anode body such as via attachment at an end of the second portion of the first anode lead.

BACKGROUND OF THE INVENTION

Solid electrolytic capacitors (e.g., tantalum capacitors) have been amajor contributor to the miniaturization of electronic circuits and havemade possible the application of such circuits in extreme environments.The anode of a typical solid electrolytic capacitor includes a porousanode body, with an anode lead extending beyond the anode body andconnected to an anode termination of the capacitor. The anode can beformed by first pressing a tantalum powder into a pellet that is thensintered to create fused connections between individual powderparticles. One problem with many conventional solid electrolyticcapacitors is that the small particle size of the tantalum particles candecrease the volumetric contact between the anode body and the anodelead. In fact, it can be difficult to find many points of contactbetween the anode lead and the powder particles. When the contact areabetween the anode body and the anode lead is decreased, there is acorresponding increase in resistance where the anode lead and the anodemeet. This increased equivalent series resistance (ESR) results in acapacitor exhibiting decreased electrical capabilities. On the otherhand, as the diameter of an anode lead is increased, the internalresistance in the anode lead itself increases, and this increase ininternal resistance can counteract any improvement (decrease) in ESRseen as the result of increasing the points of contact between the anodebody and the anode lead.

As such, a need currently exists for an improved solid electrolyticcapacitor that finds a balance between the benefit of increased pointsof contact between the anode body and the anode lead without thenegative effects of increased resistance in the lead itself as itsdiameter increases, thereby significantly improving electricalcapabilities of the capacitor by achieving ultralow ESR levels.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a solidelectrolytic capacitor is disclosed that comprises a capacitor element.The capacitor element comprises a sintered, porous anode body; a firstanode lead; a second anode lead; a dielectric layer overlying thesintered porous anode body; and a cathode overlying the dielectric layerthat includes a solid electrolyte. A first portion of the first anodelead is embedded within the porous anode body and a second portion ofthe first anode lead extends from a surface of the porous anode body ina longitudinal direction. Further, the second anode lead is positionedexternal to the porous anode body.

In accordance with another embodiment of the present invention, a methodfor forming a solid electrolytic capacitor comprising a sintered, porousanode body is disclosed. The method comprises positioning a firstportion of a first anode lead within a powder formed from a valve metalcomposition such that a second portion of the first anode lead extendsfrom a surface of the anode body in a longitudinal direction; compactingthe powder around the first portion of the first anode lead; sinteringthe compacted powder and the first portion of the first anode lead toform the porous anode body; positioning a second anode lead external tothe porous anode body; and welding the second anode lead to an anodetermination to form an electrical connection between the second anodelead and the anode termination.

Other features and aspects of the present invention are set forth ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a perspective view of one embodiment of the electrolyticcapacitor element of the present invention;

FIG. 2 is a front view of the electrolytic capacitor element of FIG. 1;

FIG. 3 is a top view of the electrolytic capacitor element of FIG. 1;

FIG. 4 is a perspective view of an electrolytic capacitor of the presentinvention that incorporates the capacitor element of FIGS. 1-3;

FIG. 5 is a perspective view of another embodiment of the electrolyticcapacitor element of the present invention;

FIG. 6 is a front view of the capacitor element of FIG. 5;

FIG. 7 is a top view of the capacitor element of FIG. 5;

FIG. 8 is a perspective view of an electrolytic capacitor of the presentinvention that incorporates the capacitor element of FIGS. 5-7;

FIG. 9 is a perspective view of one embodiment of the electrolyticcapacitor element of the present invention;

FIG. 10 is a front view of the electrolytic capacitor of FIG. 9; and

FIG. 11 is a top view of the electrolytic capacitor of FIG. 9.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended to limit the broader aspects of the present invention.Generally speaking, the present invention is directed to a solidelectrolytic capacitor containing a capacitor element that includes asintered porous anode body, a dielectric layer overlying the sinteredporous anode body, and a cathode overlying the dielectric layer thatincludes a solid electrolyte. The capacitor element also includes ananode lead assembly that contains a first anode lead and a second anodelead.

In one embodiment, the first anode lead can have a thickness that can belarger than a thickness of the second anode lead, such as when the firstanode lead and second anode lead are both made of tantalum. Forinstance, the first anode lead can have a thickness/diameter of fromabout 100 micrometers to about 2000 micrometers, while the second anodelead can have a thickness/diameter of from about 10 micrometers to about1800 micrometers. In addition, the second anode lead can have athickness/diameter that is from about 10% to about 90% of thethickness/diameter of the first anode lead. Meanwhile, in otherembodiments, the first anode lead and the second anode lead can havegenerally the same thickness, or the second anode lead can have athickness that is larger or smaller than the thickness of the firstanode lead, such as when the first anode lead is made of tantalum andthe second anode lead is made of a non-tantalum material (e.g.,stainless steel, nickel, or a nickel-iron alloy). The thickness of thenon-tantalum material depends on the particular non-tantalum materialselected and its melting point. For instance, the first anode lead andthe second anode lead can each have a thickness/diameter of from about100 micrometers to about 2000 micrometers; the first anode lead can havea thickness/diameter of from about 100 micrometers to about 2000micrometers, while the second anode lead can have a thickness/diameterof from about 100 micrometers to about 2500 micrometers; or the firstanode lead can have a thickness/diameter of from about 100 micrometersto about 2000 micrometers, while the second anode lead can have athickness/diameter of from about 10 micrometers to about 1800micrometers.

Regardless of the diameters of the first and second anode lead wires, aportion of the first anode lead is embedded in the porous anode body,and a second portion of the first anode lead extends from a surfacethereof in a longitudinal direction. Meanwhile, the second anode lead iselectrically connected to the anode body for connection to an anodetermination. In one embodiment, the second anode lead can be directlyconnected to a surface of the anode body. In another embodiment, thesecond anode lead can be indirectly connected to the anode body such asvia attachment at an end of the second portion of the first anode lead.

The present inventors have found that when the first anode lead has alarger thickness/diameter than the second anode lead, the area ofcontact between the embedded portion of the first anode lead and theanode body is increased, thus reducing ESR by decreasing the resistanceat the points of contact between the anode lead and the anode body.However, as the thickness/diameter of an anode lead increases, theinternal resistance of the anode lead also increases. In order to reducethe impact of the increased internal resistance of the first anode leadresulting from the increase in the thickness/diameter of the first anodelead, the length of the external (second) portion of the first anodelead is minimized and a second anode lead utilizing a smaller diameteris used as a carrier wire during processing and also for connection tothe anode termination. The second portion of the first anode lead canhave a length of from about 0 micrometers to about 5000 micrometers,while the second anode lead can have a length of from about 1 micrometerto about 20 millimeters. With such a two anode lead configuration, thepresent inventors have found that the ESR of the resulting capacitor canbe reduced.

Further, by connecting the second anode lead to the anode termination,such as when the second anode lead extends from an end of the secondportion of the first anode lead, less energy can be used during laserwelding due to the reduced thickness/diameter of the second anode leadcompared to the first anode lead. Further, the use of a smaller diametersecond anode lead facilitates the use of laser welding when a largerdiameter first anode lead is used, where the diameter of the first anodelead is so large that successful laser welding of the first anode leadto an anode termination would not be possible. In addition, the easewith which the second anode lead is connected to the anode terminationvia resistance welding can also be improved. Meanwhile, if conductiveadhesives are utilized to make the connection to the anode termination,a lesser amount of adhesive can be used due to the smallerthickness/diameter of the second anode lead as compared to the firstanode lead. Also, by utilizing a second anode lead having a smallerthickness/diameter than the first anode lead, other processing steps canbe simplified because a lead having a smaller thickness/diameter iseasier to manipulate than a lead having a larger thickness/diameter, andthe overall stability of the anode lead assembly can be increasedbecause there is less risk that the second anode lead will bend due toits smaller thickness/diameter when compared to the first anode lead.Moreover, using a second anode lead having a smaller thickness/diameterto carry the anodes during chemical processes such as anodization andcathode buildup reduces material costs, as a portion of the second anodelead (e.g., carrier wire) is eventually trimmed away from the capacitoritself and is not needed as a component of the final capacitor product.

On the other hand, as discussed above, the present inventors have alsofound that utilizing a second anode lead that is made from a materialthat is different from the first anode lead can reduce the costsassociated with forming the capacitors of the present disclosure, suchas when the first anode lead is made of tantalum and the second anodelead is made of stainless steel, nickel, or a nickel-iron alloy. In suchembodiments, the second anode lead can have the same thickness/diameteror the second anode lead can have a thickness/diameter that is eitherlarger or smaller than the thickness/diameter the first anode lead,which can be made of tantalum. In such embodiments, using a non-tantalumsecond anode lead to carry the anodes during chemical processes such asanodization and cathode buildup can reduce material costs. For instance,as a portion of the second anode lead (e.g., carrier wire) is eventuallytrimmed away from the capacitor itself and is not needed as a componentof the final capacitor product, a less expensive material can be used ascompared to the first anode lead.

Various embodiments of the present invention will now be described inmore detail.

I. Anode

The porous anode body is typically formed from a valve metal compositionhaving a high specific charge, such as about 2,000 μF*V/g or more, insome embodiments about 5,000 μF*V/g or more, in some embodiments about10,000 μF*V/g or more. For instance, such powders can have a specificcharge of from about 10,000 to about 600,000 μF*V/g, in some embodimentsfrom about 40,000 to about 500,000 μF*V/g, in some embodiments fromabout 70,000 to about 400,000 μF*V/g, in some embodiments from about100,000 to about 350,000 μF*V/g, and in some embodiments, from about150,000 to about 300,000 μF*V/g. As is known in the art, the specificcharge may be determined by multiplying capacitance by the anodizingvoltage employed, and then dividing this product by the weight of theanodized electrode body.

The valve metal composition contains a valve metal (i.e., a metal thatis capable of oxidation) or a valve metal-based compound, such astantalum, niobium, aluminum, hafnium, titanium, alloys thereof, oxidesthereof, nitrides thereof, and so forth. For example, the valve metalcomposition may contain an electrically conductive oxide of niobium,such as niobium oxide having an atomic ratio of niobium to oxygen of1:1.0±1.0, in some embodiments 1:1.0±0.3, in some embodiments 1:1.0±0.1,and in some embodiments, 1:1.0±0.05. For example, the niobium oxide maybe NbO_(0.7), NbO_(1.0), NbO_(1.1), and NbO₂. In a preferred embodiment,the composition contains NbO_(1.0), which is a conductive niobium oxidethat may remain chemically stable even after sintering at hightemperatures. Examples of such valve metal oxides are described in U.S.Pat. No. 6,322,912 to Fife; U.S. Pat. No. 6,391,275 to Fife et al.; U.S.Pat. No. 6,416,730 to Fife et al.; U.S. Pat. No. 6,527,937 to Fife; U.S.Pat. No. 6,576,099 to Kimmel, et al.; U.S. Pat. No. 6,592,740 to Fife,et al.; and U.S. Pat. No. 6,639,787 to Kimmel, et al.; and U.S. Pat. No.7,220,397 to Kimmel, et al., as well as U.S. Patent ApplicationPublication Nos. 2005/0019581 to Schnitter; 2005/0103638 to Schnitter,et al.; 2005/0013765 to Thomas, et al., all of which are incorporatedherein in their entirety by reference thereto for all purposes.

To form the anode, a powder of the valve metal composition is generallyemployed. The powder may contain particles any of a variety of shapes,such as nodular, angular, flake, etc., as well as mixtures thereof.Particularly suitable powders are tantalum powders available from CabotCorp. (e.g., C255 flake powder, TU4D flake/nodular powder, etc.) and H.C. Starck (e.g., NH175 nodular powder). Although not required, thepowder may be agglomerated using any technique known in the art, such asthrough heat treatment. Prior to forming the powder into the shape of ananode, it may also be optionally mixed with a binder and/or lubricant toensure that the particles adequately adhere to each other when pressedto form the anode body. The resulting powder may then be compacted toform a pellet using any conventional powder press device. For example, apress mold may be employed that is a single station compaction presscontaining a die and one or multiple punches. Alternatively, anvil-typecompaction press molds may be used that use only a die and single lowerpunch. Single station compaction press molds are available in severalbasic types, such as cam, toggle/knuckle and eccentric/crank presseswith varying capabilities, such as single action, double action,floating die, movable platen, opposed ram, screw, impact, hot pressing,coining or sizing.

Regardless of its particular composition, the powder is compacted arounda first portion 30 a of a first anode lead 30 so that a second portion30 b of the first anode lead 30 extends from the compacted porous anodebody 33, as shown in FIGS. 1 and 4 and as will be discussed in moredetail below. In one particular embodiment, a press mold may be employedthat includes a die having two or more portions (e.g., upper and lowerportions). During use, the portions of the die may be placed adjacent toeach other so that their walls are substantially aligned to form a diecavity having the desired shape of the anode. Before, during, and/orafter loading a certain quantity of powder into the die cavity, thefirst anode lead 30 may be embedded therein. The die may define a singleor multiple slots that allow for the insertion of the anode lead. Afterfilling the die with powder and embedding the first anode lead therein,the die cavity may then be closed and subjected to compressive forces bya punch. Typically, the compressive forces are exerted in a directionthat is either generally parallel or generally perpendicular to thelength of the first anode lead, which extends along a longitudinal axis(i.e., the z-axis in FIGS. 1 and 4). This forces the particles intoclose contact with the first anode lead and creates a stronglead-to-powder bond.

Any binder/lubricant may be removed after pressing by heating the pelletunder vacuum at a certain temperature (e.g., from about 150° C. to about500° C.) for several minutes. Alternatively, the binder/lubricant mayalso be removed by contacting the pellet with an aqueous solution, suchas described in U.S. Pat. No. 6,197,252 to Bishop, et al., which isincorporated herein in its entirety by reference thereto for allpurposes. Thereafter, the porous anode body is sintered to form aporous, integral mass. The pellet is typically sintered at a temperatureof from about 1200° C. to about 2000° C., in some embodiments from about1300° C. to about 1900° C., and in some embodiments, from about 1500° C.to about 1800° C., for a time of from about 5 minutes to about 100minutes, and in some embodiments, from about 30 minutes to about 60minutes. If desired, sintering may occur in an atmosphere that limitsthe transfer of oxygen atoms to the anode. For example, sintering mayoccur in a reducing atmosphere, such as in a vacuum, inert gas,hydrogen, etc. The reducing atmosphere may be at a pressure of fromabout 10 Torr to about 2000 Torr, in some embodiments from about 100Torr to about 1000 Torr, and in some embodiments, from about 100 Torr toabout 930 Torr. Mixtures of hydrogen and other gases (e.g., argon ornitrogen) may also be employed.

In the particular embodiments shown in FIGS. 1-8, the sintered, porousanode body 33 is in the shape of a rectangular pellet. In addition tohaving a rectangular shape, however, the anode can have a cubed,cylindrical, circular, or any other geometric shape. The anode may alsobe “fluted” in that it may contain one or more furrows, grooves,depressions, or indentations to increase the surface to volume ratio tominimize ESR and extend the frequency response of the capacitor. Such“fluted” anodes are described, for instance, in U.S. Pat. No. 6,191,936to Webber, et al.; U.S. Pat. No. 5,949,639 to Maeda, et al.; and U.S.Pat. No. 3,345,545 to Bourgault et al., as well as U.S. PatentApplication Publication No. 2005/0270725 to Hahn, et al., all of whichare incorporated herein in their entirety by reference thereto for allpurposes.

II. Dielectric

A dielectric also overlies or coats the anode body. The dielectric maybe formed by anodically oxidizing (“anodizing”) the sintered anode sothat a dielectric layer is formed over and/or within the anode body. Forexample, a tantalum (Ta) anode body may be anodized to tantalumpentoxide (Ta₂O₅). Typically, anodization is performed by initiallyapplying a solution to the anode body, such as by dipping the anode bodyinto the electrolyte. A solvent is generally employed, such as water(e.g., deionized water). To enhance ionic conductivity, a compound maybe employed that is capable of dissociating in the solvent to form ions.Examples of such compounds include, for instance, acids, such asdescribed below with respect to the electrolyte. For example, an acid(e.g., phosphoric acid) may constitute from about 0.01 wt. % to about 5wt. %, in some embodiments from about 0.05 wt. % to about 0.8 wt. %, andin some embodiments, from about 0.1 wt. % to about 0.5 wt. % of theanodizing solution. If desired, blends of acids may also be employed.

A current is passed through the anodizing solution to form thedielectric layer. The value of the formation voltage manages thethickness of the dielectric layer. For example, the power supply may beinitially set up at a galvanostatic mode until the required voltage isreached. Thereafter, the power supply may be switched to apotentiostatic mode to ensure that the desired dielectric thickness isformed over the entire surface of the anode body. Of course, other knownmethods may also be employed, such as pulse or step potentiostaticmethods. The voltage at which anodic oxidation occurs typically rangesfrom about 4 to about 250 V, and in some embodiments, from about 9 toabout 200 V, and in some embodiments, from about 20 to about 150 V.During oxidation, the anodizing solution can be kept at an elevatedtemperature, such as about 30° C. or more, in some embodiments fromabout 40° C. to about 200° C., and in some embodiments, from about 50°C. to about 100° C. Anodic oxidation can also be done at ambienttemperature or lower. The resulting dielectric layer may be formed on asurface of the anode body and within its pores.

Although not required, in certain embodiments, the dielectric layer maypossess a differential thickness throughout the anode body in that itpossesses a first portion that overlies an external surface of the anodebody and a second portion that overlies an interior surface of the anodebody. In such embodiments, the first portion is selectively formed sothat its thickness is greater than that of the second portion. It shouldbe understood, however, that the thickness of the dielectric layer neednot be uniform within a particular region. Certain portions of thedielectric layer adjacent to the external surface may, for example,actually be thinner than certain portions of the layer at the interiorsurface, and vice versa. Nevertheless, the dielectric layer may beformed such that at least a portion of the layer at the external surfacehas a greater thickness than at least a portion at the interior surface.Although the exact difference in these thicknesses may vary depending onthe particular application, the ratio of the thickness of the firstportion to the thickness of the second portion is typically from about1.2 to about 40, in some embodiments from about 1.5 to about 25, and insome embodiments, from about 2 to about 20.

To form a dielectric layer having a differential thickness, amulti-stage process is generally employed. In each stage of the process,the sintered anode body is anodically oxidized (“anodized”) to form adielectric layer (e.g., tantalum pentoxide). During the first stage ofanodization, a relatively small forming voltage is typically employed toensure that the desired dielectric thickness is achieved for the innerregion, such as forming voltages ranging from about 1 to about 90 volts,in some embodiments from about 2 to about 50 volts, and in someembodiments, from about 5 to about 20 volts. Thereafter, the sinteredbody may then be anodically oxidized in a second stage of the process toincrease the thickness of the dielectric to the desired level. This isgenerally accomplished by anodizing in an electrolyte at a highervoltage than employed during the first stage, such as at formingvoltages ranging from about 50 to about 350 volts, in some embodimentsfrom about 60 to about 300 volts, and in some embodiments, from about 70to about 200 volts. During the first and/or second stages, theelectrolyte may be kept at a temperature within the range of from about15° C. to about 95° C., in some embodiments from about 20° C. to about90° C., and in some embodiments, from about 25° C. to about 85° C.

The electrolytes employed during the first and second stages of theanodization process may be the same or different. Typically, however, itis desired to employ different solutions to help better facilitate theattainment of a higher thickness at the outer portions of the dielectriclayer. For example, it may be desired that the electrolyte employed inthe second stage has a lower ionic conductivity than the electrolyteemployed in the first stage to prevent a significant amount of oxidefilm from forming on the internal surface of anode body. In this regard,the electrolyte employed during the first stage may contain an acidiccompound, such as hydrochloric acid, nitric acid, sulfuric acid,phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.Such an electrolyte may have an electrical conductivity of from about0.1 to about 100 mS/cm, in some embodiments from about 0.2 to about 20mS/cm, and in some embodiments, from about 1 to about 10 mS/cm,determined at a temperature of 25° C. The electrolyte employed duringthe second stage typically contains a salt of a weak acid so that thehydronium ion concentration increases in the pores as a result of chargepassage therein. Ion transport or diffusion is such that the weak acidanion moves into the pores as necessary to balance the electricalcharges. As a result, the concentration of the principal conductingspecies (hydronium ion) is reduced in the establishment of equilibriumbetween the hydronium ion, acid anion, and undissociated acid, thusforms a poorer-conducting species. The reduction in the concentration ofthe conducting species results in a relatively high voltage drop in theelectrolyte, which hinders further anodization in the interior while athicker Oxide layer is being built up on the outside to a higherformation voltage in the region of continued high conductivity. Suitableweak acid salts may include, for instance, ammonium or alkali metalsalts (e.g., sodium, potassium, etc.) of boric acid, boronic acid,acetic acid, oxalic acid, lactic acid, adipic acid, etc. Particularlysuitable salts include sodium tetraborate and ammonium pentaborate. Suchelectrolytes typically have an electrical conductivity of from about 0.1to about 20 mS/cm, in some embodiments from about 0.5 to about 10 mS/cm,and in some embodiments, from about 1 to about 5 mS/cm, determined at atemperature of 25° C.

If desired, each stage of anodization may be repeated for one or morecycles to achieve the desired dielectric thickness. Furthermore, theanode body may also be rinsed or washed with another solvent (e.g.,water) after the first and/or second stages to remove the electrolyte.

III. Solid Electrolyte

The capacitor element also contains a solid electrolyte that functionsas the cathode for the capacitor. A manganese dioxide solid electrolytemay, for instance, be formed by the pyrolytic decomposition of manganousnitrate (Mn(NO₃)₂). Such techniques are described, for instance, in U.S.Pat. No. 4,945,452 to Sturmer, et al., which is incorporated herein inits entirety by reference thereto for all purposes.

Alternatively, the solid electrolyte may be formed from one or moreconductive polymer layers. The conductive polymer(s) employed in suchlayers are typically π-conjugated and have electrical conductivity afteroxidation or reduction, such as an electrical conductivity of at leastabout 1 μS cm⁻¹ after oxidation. Examples of such π-conjugatedconductive polymers include, for instance, polyheterocycles (e.g.,polypyrroles, polythiophenes, polyanilines, etc.), polyacetylenes,poly-p-phenylenes, polyphenolates, and so forth. Particularly suitableconductive polymers are substituted polythiophenes having the followinggeneral structure:

wherein,

T is O or S;

D is an optionally substituted C₁ to C₅ alkylene radical (e.g.,methylene, ethylene, n-propylene, n-butylene, n-pentylene, etc.);

R₇ is a linear or branched, optionally substituted C₁ to C₁₈ alkylradical (e.g., methyl, ethyl, n- or iso-propyl, n-, iso-, sec- ortert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl,1-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,2,2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl,n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl,n-octadecyl, etc.); optionally substituted C₅ to C₁₂ cycloalkyl radical(e.g., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononylcyclodecyl, etc.); optionally substituted C₆ to C₁₄ aryl radical (e.g.,phenyl, naphthyl, etc.); optionally substituted C₇ to C₁₈ aralkylradical (e.g., benzyl, o-, m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-,3,5-xylyl, mesityl, etc.); optionally substituted C₁ to C₄ hydroxyalkylradical, or hydroxyl radical; and

q is an integer from 0 to 8, in some embodiments, from 0 to 2, and inone embodiment, 0; and

n is from 2 to 5,000, in some embodiments from 4 to 2,000, and in someembodiments, from 5 to 1,000. Example of substituents for the radicals“D” or “R₇” include, for instance, alkyl, cycloalkyl, aryl, aralkyl,alkoxy, halogen, ether, thioether, disulphide, sulfoxide, sulfone,sulfonate, amino, aldehyde, keto, carboxylic acid ester, carboxylicacid, carbonate, carboxylate, cyano, alkylsilane and alkoxysilanegroups, carboxylamide groups, and so forth.

Particularly suitable thiophene polymers are those in which “D” is anoptionally substituted C₂ to C₃ alkylene radical. For instance, thepolymer may be optionally substituted poly(3,4-ethylenedioxythiophene),which has the following general structure:

Methods for forming conductive polymers, such as described above, arewell known in the art. For instance, U.S. Pat. No. 6,987,663 to Merker,et al., which is incorporated herein in its entirety by referencethereto for all purposes, describes various techniques for formingsubstituted polythiophenes from a monomeric precursor. The monomericprecursor may, for instance, have the following structure:

wherein,

T, D, R₇, and q are defined above. Particularly suitable thiophenemonomers are those in which “D” is an optionally substituted C₂ to C₃alkylene radical. For instance, optionally substituted3,4-alkylenedioxythiophenes may be employed that have the generalstructure:

wherein, R₇ and q are as defined above. In one particular embodiment,“q” is 0. One commercially suitable example of 3,4-ethylenedioxthiopheneis available from Heraeus Clevios under the designation Clevios™ M.Other suitable monomers are also described in U.S. Pat. No. 5,111,327 toBlohm, et al. and U.S. Pat. No. 6,635,729 to Groenendaal, et al., whichare incorporated herein in their entirety by reference thereto for allpurposes. Derivatives of these monomers may also be employed that are,for example, dimers or trimers of the above monomers. Higher molecularderivatives, i.e., tetramers, pentamers, etc. of the monomers are alsosuitable for use in the present invention. The derivatives may be madeup of identical or different monomer units and used in pure form and ina mixture with one another and/or with the monomers. Oxidized or reducedforms of these precursors may also be employed.

The thiophene monomers are chemically polymerized in the presence of anoxidative catalyst. The oxidative catalyst typically includes atransition metal cation, such as iron(III), copper(II), chromium(VI),cerium(IV), manganese(IV), manganese(VII), or ruthenium(III) cations,and etc. A dopant may also be employed to provide excess charge to theconductive polymer and stabilize the conductivity of the polymer. Thedopant typically includes an inorganic or organic anion, such as an ionof a sulfonic acid. In certain embodiments, the oxidative catalystemployed in the precursor solution has both a catalytic and dopingfunctionality in that it includes a cation (e.g., transition metal) andan anion (e.g., sulfonic acid). For example, the oxidative catalyst maybe a transition metal salt that includes iron(III) cations, such asiron(III) halides (e.g., FeCl₃) or iron(III) salts of other inorganicacids, such as Fe(ClO₄)₃ or Fe₂(SO₄)₃ and the iron(III) salts of organicacids and inorganic acids comprising organic radicals. Examples of iron(III) salts of inorganic acids with organic radicals include, forinstance, iron(III) salts of sulfuric acid monoesters of C₁ to C₂₀alkanols (e.g., iron(III) salt of lauryl sulfate). Likewise, examples ofiron(III) salts of organic acids include, for instance, iron(III) saltsof C₁ to C₂₀ alkane sulfonic acids (e.g., methane, ethane, propane,butane, or dodecane sulfonic acid); iron (III) salts of aliphaticperfluorosulfonic acids (e.g., trifluoromethane sulfonic acid,perfluorobutane sulfonic acid, or perfluorooctane sulfonic acid); iron(III) salts of aliphatic C₁ to C₂₀ carboxylic acids (e.g.,2-ethylhexylcarboxylic acid); iron (III) salts of aliphaticperfluorocarboxylic acids (e.g., trifluoroacetic acid or perfluorooctaneacid); iron (III) salts of aromatic sulfonic acids optionallysubstituted by C₁ to C₂₀ alkyl groups (e.g., benzene sulfonic acid,o-toluene sulfonic acid, p-toluene sulfonic acid, or dodecylbenzenesulfonic acid); iron (III) salts of cycloalkane sulfonic acids (e.g.,camphor sulfonic acid); and so forth. Mixtures of these above-mentionediron(III) salts may also be used. Iron(III)-p-toluene sulfonate,iron(III)-o-toluene sulfonate, and mixtures thereof, are particularlysuitable. One commercially suitable example of iron(III)-p-toluenesulfonate is available from Heraeus Clevios under the designationClevios™ C.

Various methods may be utilized to form a conductive polymer layer. Inone embodiment, the oxidative catalyst and monomer are applied, eithersequentially or together, such that the polymerization reaction occursin situ on the anode part. Suitable application techniques that mayinclude screen-printing, dipping, electrophoretic coating, and sprayingmay be used to form a conductive polymer coating. As an example, themonomer may initially be mixed with the oxidative catalyst to form aprecursor solution. Once the mixture is formed, it may be applied to theanode part and then allowed to polymerize so that the conductive coatingis formed on the surface. Alternatively, the oxidative catalyst andmonomer may be applied sequentially. In one embodiment, for example, theoxidative catalyst is dissolved in an organic solvent (e.g., butanol)and then applied as a dipping solution. The anode part may then be driedto remove the solvent therefrom. Thereafter, the part may be dipped intoa solution containing the monomer.

Polymerization is typically performed at temperatures of from about −10°C. to about 250° C., and in some embodiments, from about 0° C. to about200° C., depending on the oxidizing agent used and desired reactiontime. Suitable polymerization techniques, such as described above, maybe described in more detail in U.S. Pat. No. 7,515,396 to Biler. Stillother methods for applying such conductive coating(s) may be describedin U.S. Pat. No. 5,457,862 to Sakata, et al., U.S. Pat. No. 5,473,503 toSakata, et al., U.S. Pat. No. 5,729,428 to Sakata, et al., and U.S. Pat.No. 5,812,367 to Kudoh, et al., which are incorporated herein in theirentirety by reference thereto for all purposes.

In addition to in situ application, a conductive polymer layer may alsobe applied in the form of a dispersion of conductive polymer particles.Although the particle size may vary, it is typically desired that theparticles possess a small diameter to increase the surface areaavailable for adhering to the anode part. For example, the particles mayhave an average diameter of from about 1 nanometer to about 500nanometers, in some embodiments from about 5 nanometers to about 400nanometers, and in some embodiments, from about 10 nanometers to about300 nanometers. The D₉₀ value of the particles (particles having adiameter of less than or equal to the D₉₀ value constitute 90% of thetotal volume of all of the solid particles) may be about 15 micrometersor less, in some embodiments about 10 micrometers or less, and in someembodiments, from about 1 nanometer to about 8 micrometers. The diameterof the particles may be determined using known techniques, such as byultracentrifuge, laser diffraction, etc.

The formation of the conductive polymer into a particulate form may beenhanced by using a separate counterion to counteract the positivecharge carried by the substituted polythiophene. In some cases, thepolymer may possess positive and negative charges in the structuralunit, with the positive charge being located on the main chain and thenegative charge optionally on the substituents of the radical “R”, suchas sulfonate or carboxylate groups. The positive charges of the mainchain may be partially or wholly saturated with the optionally presentanionic groups on the radicals “R.” Viewed overall, the polythiophenesmay, in these cases, be cationic, neutral or even anionic. Nevertheless,they are all regarded as cationic polythiophenes as the polythiophenemain chain has a positive charge.

The counterion may be a monomeric or polymeric anion. Polymeric anionscan, for example, be anions of polymeric carboxylic acids (e.g.,polyacrylic acids, polymethacrylic acid, polymaleic acids, etc.);polymeric sulfonic acids (e.g., polystyrene sulfonic acids (“PSS”),polyvinyl sulfonic acids, etc.); and so forth. The acids may also becopolymers, such as copolymers of vinyl carboxylic and vinyl sulfonicacids with other polymerizable monomers, such as acrylic acid esters andstyrene. Likewise, suitable monomeric anions include, for example,anions of C₁ to C₂₀ alkane sulfonic acids (e.g., dodecane sulfonicacid); aliphatic perfluorosulfonic acids (e.g., trifluoromethanesulfonic acid, perfluorobutane sulfonic acid or perfluorooctane sulfonicacid); aliphatic C₁ to C₂₀ carboxylic acids (e.g.,2-ethyl-hexylcarboxylic acid); aliphatic perfluorocarboxylic acids(e.g., trifluoroacetic acid or perfluorooctanoic acid); aromaticsulfonic acids optionally substituted by C₁ to C₂₀ alkyl groups (e.g.,benzene sulfonic acid, o-toluene sulfonic acid, p-toluene sulfonic acidor dodecylbenzene sulfonic acid); cycloalkane sulfonic acids (e.g.,camphor sulfonic acid or tetrafluoroborates, hexafluorophosphates,perchlorates, hexafluoroantimonates, hexafluoroarsenates orhexachloroantimonates); and so forth. Particularly suitablecounteranions are polymeric anions, such as a polymeric carboxylic orsulfonic acid (e.g., polystyrene sulfonic acid (“PSS”)). The molecularweight of such polymeric anions typically ranges from about 1,000 toabout 2,000,000, and in some embodiments, from about 2,000 to about500,000.

When employed, the weight ratio of such counterions to substitutedpolythiophenes in a given layer is typically from about 0.5:1 to about50:1, in some embodiments from about 1:1 to about 30:1, and in someembodiments, from about 2:1 to about 20:1. The weight of the substitutedpolythiophene referred to in the above-referenced weight ratios refersto the weighed-in portion of the monomers used, assuming that a completeconversion occurs during polymerization.

The dispersion may also contain one or more binders to further enhancethe adhesive nature of the polymeric layer and also increase thestability of the particles within the dispersion. The binders may beorganic in nature, such as polyvinyl alcohols, polyvinyl pyrrolidones,polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates,polyacrylic acid esters, polyacrylic acid amides, polymethacrylic acidesters, polymethacrylic acid amides, polyacrylonitriles, styrene/acrylicacid ester, vinyl acetate/acrylic acid ester and ethylene/vinyl acetatecopolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers,polyesters, polycarbonates, polyurethanes, polyamides, polyimides,polysulfones, melamine formaldehyde resins, epoxide resins, siliconeresins or celluloses. Crosslinking agents may also be employed toenhance the adhesion capacity of the binders. Such crosslinking agentsmay include, for instance, melamine compounds, masked isocyanates orfunctional silanes, such as 3-glycidoxypropyltrialkoxysilane,tetraethoxysilane and tetraethoxysilane hydrolysate or crosslinkablepolymers, such as polyurethanes, polyacrylates or polyolefins. Othercomponents may also be included within the dispersion as is known in theart, such as dispersion agents (e.g., water), surface-active substances,etc.

If desired, one or more of the above-described application steps may berepeated until the desired thickness of the coating is achieved. In someembodiments, only a relatively thin layer of the coating is formed at atime. The total target thickness of the coating may generally varydepending on the desired properties of the capacitor. Typically, theresulting conductive polymer coating has a thickness of from about 0.2micrometers to about 50 micrometers, in some embodiments from about 0.5micrometers to about 20 micrometers, and in some embodiments, from about1 micrometers to about 5 micrometers. It should be understood that thethickness of the coating is not necessarily the same at all locations onthe anode part. Nevertheless, the average thickness of the coating onthe substrate generally falls within the ranges noted above.

The conductive polymer layer may optionally be healed. Healing may occurafter each application of a conductive polymer layer or may occur afterthe application of the entire coating. In some embodiments, theconductive polymer can be healed by dipping the part into an electrolytesolution, and thereafter applying a constant voltage to the solutionuntil the current is reduced to a preselected level. If desired, suchhealing can be accomplished in multiple steps. For example, anelectrolyte solution can be a dilute solution of the monomer, thecatalyst, and dopant in an alcohol solvent (e.g., ethanol). The coatingmay also be washed if desired to remove various byproducts, excessreagents, and so forth.

IV. External Polymer Coating

Although not required, an external polymer coating may also be appliedto the anode body and overlie the solid electrolyte. The externalpolymer coating generally contains one or more layers formed from adispersion of pre-polymerized conductive particles, such as described inmore detail above. The external coating may be able to further penetrateinto the edge region of the capacitor body to increase the adhesion tothe dielectric and result in a more mechanically robust part, which mayreduce equivalent series resistance and leakage current. Because it isgenerally intended to improve the degree of edge coverage rather toimpregnate the interior of the anode body, the particles used in theexternal coating typically have a larger size than those employed in anyoptional dispersions of the solid electrolyte. For example, the ratio ofthe average size of the particles employed in the external polymercoating to the average size of the particles employed in any dispersionof the solid electrolyte is typically from about 1.5 to about 30, insome embodiments from about 2 to about 20, and in some embodiments, fromabout 5 to about 15. For example, the particles employed in thedispersion of the external coating may have an average size of fromabout 50 nanometers to about 500 nanometers, in some embodiments fromabout 80 nanometers to about 250 nanometers, and in some embodiments,from about 100 nanometers to about 200 nanometers.

If desired, a crosslinking agent may also be employed in the externalpolymer coating to enhance the degree of adhesion to the solidelectrolyte. Typically, the crosslinking agent is applied prior toapplication of the dispersion used in the external coating. Suitablecrosslinking agents are described, for instance, in U.S. PatentPublication No. 2007/0064376 to Merker, et al. and include, forinstance, amines (e.g., diamines, triamines, oligomer amines,polyamines, etc.); polyvalent metal cations, such as salts or compoundsof Mg, Al, Ca, Fe, Cr, Mn, Ba, Ti, Co, Ni, Cu, Ru, Ce or Zn, phosphoniumcompounds, sulfonium compounds, etc. Particularly suitable examplesinclude, for instance, 1,4-diaminocyclohexane,1,4-bis(amino-methyl)cyclohexane, ethylenediamine, 1,6-hexanediamine,1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine,1,10-decanediamine, 1,12-dodecanediamine, N,N-dimethylethylenediamine,N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethyl-1,4-butanediamine, etc., as well as mixturesthereof.

The crosslinking agent is typically applied from a solution ordispersion whose pH is from 1 to 10, in some embodiments from 2 to 7, insome embodiments, from 3 to 6, as determined at 25° C. Acidic compoundsmay be employed to help achieve the desired pH level. Examples ofsolvents or dispersants for the crosslinking agent include water ororganic solvents, such as alcohols, ketones, carboxylic esters, etc. Thecrosslinking agent may be applied to the capacitor body by any knownprocess, such as spin-coating, impregnation, casting, dropwiseapplication, spray application, vapor deposition, sputtering,sublimation, knife-coating, painting or printing, for example inkjet,screen or pad printing. Once applied, the crosslinking agent may bedried prior to application of the polymer dispersion. This process maythen be repeated until the desired thickness is achieved. For example,the total thickness of the entire external polymer coating, includingthe crosslinking agent and dispersion layers, may range from about 1micrometer to about 50 micrometers, in some embodiments from about 2micrometers to about 40 micrometers, and in some embodiments, from about5 micrometers to about 20 micrometers.

V. Other Layers of the Capacitor

If desired, the capacitor may contain other layers in addition to thedielectric layer, solid electrolyte, etc. as is known in the art. Forexample, a protective coating may optionally be formed between thedielectric and solid electrolyte, such as one made of a relativelyinsulative resinous material (natural or synthetic). Such materials mayhave a specific resistivity of greater than about 10 Ω·cm, in someembodiments greater than about 100, in some embodiments greater thanabout 1,000 Ω·cm, in some embodiments greater than about 1×10⁵ Ω·cm, andin some embodiments, greater than about 1×10¹⁰ Ω·cm. Some resinousmaterials that may be utilized in the present invention include, but arenot limited to, polyurethane, polystyrene, esters of unsaturated orsaturated fatty acids (e.g., glycerides), and so forth. For instance,suitable esters of fatty acids include, but are not limited to, estersof lauric acid, myristic acid, palmitic acid, stearic acid, eleostearicacid, oleic acid, linoleic acid, linolenic acid, aleuritic acid,shellolic acid, and so forth. These esters of fatty acids have beenfound particularly useful when used in relatively complex combinationsto form a “drying oil”, which allows the resulting film to rapidlypolymerize into a stable layer. Such drying oils may include mono-, di-,and/or tri-glycerides, which have a glycerol backbone with one, two, andthree, respectively, fatty acyl residues that are esterified. Forinstance, some suitable drying oils that may be used include, but arenot limited to, olive oil, linseed oil, castor oil, tung oil, soybeanoil, and shellac. These and other protective coating materials aredescribed in more detail U.S. Pat. No. 6,674,635 to Fife, et al., whichis incorporated herein in its entirety by reference thereto for allpurposes.

If desired, the part may also be applied with a carbon layer (e.g.,graphite) and silver layer, respectively. The silver coating may, forinstance, act as a solderable conductor, contact layer, and/or chargecollector for the capacitor and the carbon coating may limit contact ofthe silver coating with the solid electrolyte. Such coatings may coversome or all of the solid electrolyte.

VI. Anode Lead Assembly

As discussed above, the electrolytic capacitor of the present inventionincludes a first anode lead and a second anode lead that form an anodelead assembly. The first and second anode leads may be formed from anyelectrically conductive material, such as tantalum, niobium, nickel,aluminum, hafnium, titanium, stainless steel, etc., as well as alloys,oxides, and/or nitrides of thereof. It should be understood that it isnot required that the first and second anode leads be formed from thesame material (e.g., tantalum). For instance, in some embodiments, thefirst anode lead can be tantalum and the second anode lead can be astainless steel, nickel, or a nickel alloy. In one particularembodiment, the second anode lead is NILO®, which is a nickel-ironalloy. The first and second anode leads may possess any desiredcross-sectional shape, such as circular, elliptical, square,rectangular, etc. Further, only one of the leads need be embedded withinthe porous anode body, and only one of the leads need be directlyconnected to an anode termination. For example, the first anode lead canhave a first portion that is embedded within the porous anode body and asecond portion that extends from a surface thereof in a longitudinaldirection. Meanwhile, the second anode lead is not embedded within theporous anode body and can be used in forming a connection to an anodetermination.

Moreover, regardless of whether or not the first anode lead and thesecond anode lead are formed form the same or different materials, thefirst anode lead can have a larger thickness/diameter than the secondanode lead to improve the bonding between the first anode lead and theparticles of the anode body, which can result in a lower ESR, while thesecond anode lead can have a smaller thickness/diameter than the firstanode lead to reduce the internal resistance of the overall anode leadassembly, which can also result in a lower ESR. Thus, the combination ofthe larger diameter first anode lead and the smaller diameter secondanode lead synergistically reduces the ESR of the capacitor. Forinstance, because the first portion of the first anode lead is embeddedwithin the anode body and has a larger diameter to increase the pointsof contact between the first anode lead and the anode body, theresistance at the points of contact is reduced. In addition, the secondportion of the first anode lead having a large diameter can extend onlya short distance from a surface of the anode body to minimize the lengthof the first anode lead having a larger diameter, which, in turn, canminimize the effect of the increased internal resistance in the lead dueto the its larger diameter. Meanwhile, the external second anode leadwhich can be used to form an electrical connection with an anodetermination, can have a small diameter than that of the first anodelead, which reduces the internal resistance of the second anode lead tominimize the ESR of the lead assembly extending from/external to theporous anode body. However, in some instances, it is to be understoodthat the first anode lead and second anode lead may also have the samethickness/diameter, or the second anode lead may have a largerthickness/diameter, such as when the first anode lead is made oftantalum and the second anode lead is made of a non-tantalum material,such as stainless steel, nickel, or a nickel-iron alloy.

As described above and shown in FIGS. 1-8, in some embodiments, such aswhen the first and second anode leads both include tantalum, or when thefirst anode lead includes tantalum and the second anode lead includes anon-tantalum material, the anode lead assembly includes a first anodelead that generally has a larger thickness/diameter than the secondanode lead. Generally, the first anode lead can have athickness/diameter D1 of from about 100 micrometers to about 2000micrometers, such as from about 200 micrometers to about 1500micrometers, such as from about 250 micrometers to about 1000micrometers. Meanwhile, the second anode lead can have athickness/diameter D2 of from about 10 micrometers to about 1800micrometers, such as from about 50 micrometers to about 1200micrometers, such as from about 100 micrometers to about 750micrometers. Further, the second anode lead can have athickness/diameter that is from about 10% to about 90% of thethickness/diameter of the first anode lead, such as from about 15% toabout 85% of the thickness/diameter of the first anode lead, such asfrom about 20% to about 80% of the thickness/diameter of the first anodelead, such as from about 25% to about 75% of the thickness/diameter ofthe first anode lead.

Meanwhile, as shown in FIGS. 9-11, in some embodiments, such as when thefirst anode lead includes tantalum and the second anode lead includes anon-tantalum material, the anode lead assembly can include a first anodelead that generally has the same thickness/diameter as the second anodelead. Thus, the first anode lead and the second anode lead can havethicknesses/diameters D1 and D2 of from about 100 micrometers to about2000 micrometers, such as from about 200 micrometers to about 1500micrometers, such as from about 250 micrometers to about 1000micrometers. It is to be understood, however, that in some instances,the second anode lead may also have a thickness/diameter D2 that islarger than the thickness/diameter D1 of the first anode lead, such thatfirst anode lead can have a thickness/diameter D1 of from about 100micrometers to about 2000 micrometers, such as from about 200micrometers to about 1500 micrometers, such as from about 250micrometers to about 1000 micrometers, while the second anode lead canhave a thickness/diameter D2 of from about 100 micrometers to about 2500micrometers, such as from about 205 micrometers to about 2000micrometers, such as from about 255 micrometers micrometers to about1500 micrometers.

Moreover, as shown in FIGS. 1, 3, 4-5, 7-8, 9, and 11, the first portion30 a of the first anode lead 30 (i.e., the portion of the first anodelead that extends from a surface of the porous anode body in alongitudinal direction) can have a length (L1) in the longitudinal (z)direction that is shorter than the length (L2) of the second anode lead40 in the longitudinal (z) direction. The length L1 of the secondportion of the first anode lead 30 is minimized to reduce the ESR of thecapacitor that can be attributed to the increased internal resistance ofthe first anode lead 30 due to its larger diameter and to enhance thestability of the lead assembly 50 by reducing the risk of bending due tothe weight of the first anode lead 30. Thus, the second portion of thefirst anode lead can have a length greater than 0 micrometers to about5000 micrometers, such as from about 1 micrometer to about 2500micrometers, such as from about 10 micrometers to about 1250micrometers, while the second anode lead can have a length of from about1 micrometer to about 20 millimeters, such as from about 100 micrometersto about 15 millimeters, such as from about 1000 micrometers to about 10millimeters.

In addition, it should be understood that the anode lead assembly 50 canhave various configurations depending on where the second anode lead isconnected to the porous anode body. In one embodiment, the second anodelead can be directly connected to an exterior surface of the porousanode body such that the second anode lead is adjacent to and is inelectrical contact with the second portion of the first anode lead thatextends from the same surface of the porous anode body in a longitudinaldirection, as shown in FIG. 1. The second anode lead can be connected tothe surface of the porous anode body any suitable method such as byresistance welding, laser welding, or a conductive adhesive. In anotherembodiment, the second anode lead can be directly connected to thesecond portion of the first anode lead, such as at the end of the secondportion of the first anode lead, as shown in FIG. 5, such that thesecond anode lead extends from the end of the second portion of thefirst anode lead in a longitudinal direction. The second anode lead canbe connected to the end of the second portion of the first anode lead byany suitable method such as by resistance welding, laser welding, or aconductive adhesive.

VII. Terminations

Regardless of the particular design or manner in which the capacitor isformed, it can be connected to terminations as is well known in the art.For example, anode and cathode terminations may be electricallyconnected to the second anode lead and the cathode, respectively. Thespecific configuration of the terminations may vary as is well known inthe art. Although not required, in one embodiment, as shown in FIGS. 4and 8, for example, the cathode termination 44 can contain a planarportion 45 in electrical contact with a lower surface 39 of thecapacitor element and an upstanding portion 46 positioned substantiallyperpendicular to the planar portion 45 and in electrical contact with arear surface 38 of the capacitor element. To attach the capacitorelement to the cathode termination, a conductive adhesive may beemployed as is known in the art. The conductive adhesive may include,for instance, conductive metal particles contained with a resincomposition. The metal particles may be silver, copper, gold, platinum,nickel, zinc, bismuth, etc. The resin composition may include athermoset resin (e.g., epoxy resin), curing agent (e.g., acidanhydride), and coupling agent (e.g., silane coupling agents). Suitableconductive adhesives are described in U.S. Patent ApplicationPublication No. 2006/0038304 to Osako, et al., which is incorporatedherein in its entirety by reference thereto for all purposes.

Referring again to FIGS. 4 and 8, although not required, the anodetermination 35 may likewise contain a planar portion 41 and anupstanding portion 42. The upstanding portion 42 may contain a regionthat carries the second anode lead 40 of the present invention. Forexample, the region may possess a slot 43 for receiving the second anodelead 40. The slot may have any desired shape, and can be U-shaped,V-shaped, circular, rectangular, square, stepped, etc. for furtherenhancing surface contact and mechanical stability of the second anodelead 40 at the anode termination 35. For instance, the geometry of theslot may match the geometry of the second anode lead 40. The secondanode lead 40 can be electrically connected to the anode termination 35by any suitable technique, such as by laser welding, by resistancewelding, or the use of conductive adhesives, etc. Regardless of theparticular welding technique used to connect the second anode lead 40 tothe anode termination 35, the amount of energy required to form asufficient weld is reduced when compared to the amount of energy thatwould be required if the larger diameter first anode lead 30 wasdirectly connected to the anode termination 35. Thus, by utilizing asmaller second anode lead 40 to serve as the direct connection to theanode termination 35, the benefit of embedding a relatively thick firstanode lead 30 in the porous anode body 33 can still be realized (i.e.,improved contact with the porous anode body to reduce ESR), yet thewelding process to form an electrical connection with an anodetermination can be carried out in a more efficient and cost-effectivemanner due to the reduced thickness/diameter of the second anode lead40.

Further, once the capacitor element is formed and is attached to theterminations as discussed above, it can be enclosed within a resincasing, which may then be filled with silica or any other knownencapsulating material. The width and length of the case may varydepending on the intended application. However, the overall thickness ofthe casing is typically small so that the resultant assembly may bereadily incorporated into low profile products (e.g., “IC cards”). Forexample, the thickness of the casing may range from about 4.0millimeters or less, in some embodiments, from about 100 micrometers toabout 2.5 millimeters, and in some embodiments, from about 150micrometers to about 2.0 millimeters. Suitable casings may include, forinstance, “A”, “B”, “H”, or “T” cases (AVX Corporation). Afterencapsulation, exposed portions of the respective anode and cathodeterminations may be aged, screened, and trimmed. If desired, the exposedportions may be optionally bent twice along the outside of the casing(e.g., at an approximately 90° angle).

Turning now to FIGS. 1-11, various embodiments of the solid electrolyticcapacitor of the present invention are discussed in more detail.

Referring now to FIG. 1, one particular embodiment of a capacitorelement 100 that is formed from a porous anode body 33 and an anode leadassembly 50 including first anode lead 30 and second anode lead 40 isshown. Generally, FIG. 1 is a perspective view of the porous anode body33 that is formed around first anode lead 30 and shows the arrangementand dimensions of the porous anode body 33, the first anode lead 30, andthe second anode lead 40. For instance, the porous anode body 33 canhave a first side surface 31, a second side surface 32, a front surface36, a rear surface 37, an upper surface 38, and a lower surface 39. Theporous anode body 33 can also have a width W that can refer, forexample, to the width of the front surface 36 along the x-axis, and aheight H that can refer, for example, to the height or thickness of thefront surface 36 along the y-axis. The width W of the front surface 36of the porous anode body 33 can range from about 200 micrometers toabout 8000 micrometers, in some embodiments, from about 400 micrometersto 6000 micrometers, and in some embodiments, from about 600 micrometersto about 4000 micrometers. Additionally, the height H of the frontsurface 36 of the porous anode body 33 can range from about 200micrometers to about 8000 micrometers, in some embodiments from about400 micrometers to about 6000 micrometers, and in some embodiments fromabout 600 micrometers to about 4000 micrometers.

Further, as shown in FIG. 1, the first anode lead 30 can have a firstportion 30 a that extends from a surface of the porous anode body 33,such as front surface 36, and a second portion 30 b that is positionedwithin the anode body 33. The thickness/diameter of the first anode lead30 may vary depending on the overall size of the anode body 33. In anyevent, the larger the thickness/diameter D1 (see FIG. 2), the larger thenumber of points of contact between the porous anode body 33 and theanode lead 30 along embedded second portion 30 b, which results in alower ESR and improved electrical capabilities of the capacitor. Thedimensions of the first anode lead 30 are discussed in section VI above.

As shown in FIGS. 1-3, the first anode lead 30 extends from the frontsurface 36 of the porous anode body 33; however, it should be understoodthat the first anode lead 30 may also extend from any other surface ofthe porous anode body 33. Further, the first portion 30 a of the firstanode lead 30 that extends from a surface of the porous anode body 33can have a thickness D1 (see FIG. 2 showing the front view of thecapacitor element 100), which, as mentioned above, also refers to thethickness of the second portion 30 b of the first anode lead 30 that isembedded within the porous anode body 33.

Additionally, the capacitor element 100 of FIG. 1 also includes a secondanode lead 40 as part of its anode lead assembly 50. As shown, thesecond anode lead 40 has a thickness/diameter D2 (see FIG. 2) that issmaller than the thickness/diameter of D1. In the particular capacitorelement 100 of FIG. 1, the second anode lead 40 can be connecteddirectly to the front surface 36 of the porous anode body via anysuitable method as discussed in detail above. Further, the second anodelead 40 is adjacent to and in electrical contact with the first portion30 a of the first anode lead 30, which is the portion that extends fromthe front surface 36 of the porous anode body in the longitudinal (z)direction, as shown in FIGS. 1-3. The dimensions of the second anodelead 40 are discussed in section VI above.

Initially, as shown in FIG. 1, the length L1 of the first portion 30 aof the first anode lead 30 can be shorter than the length L2 of thesecond anode lead 40. The second anode lead 40 is used as a carrier wireduring chemical processing, such as anodization and cathode buildup, aswell as during any other phases of the assembly of the capacitor. Thevarious ranges for the lengths of each of the anode leads are discussedin detail in section VI above, and generally the length L1 of the firstportion 30 a of the first anode lead 30 is less than the length L2 ofthe second anode lead 40 to minimize the internal resistance attributedto the first anode lead 30, which, in turn, reduces the ESR. The shorterlength of the first anode lead 30 can also enhance the stability of thelead assembly 50 during processing by reducing the weight of the anodelead assembly 50, which can limit the tendency of the anode leadassembly 50 to bend compared to when a larger diameter anode lead havinga longer length is utilized. Further, the amount of material requiredfor the first anode lead 30 is reduced, which is more cost efficient.Meanwhile, the second anode lead 40, at least initially, has a length L2that is longer than the length L1 of the first anode lead 30 so that thesecond anode lead 40 having a smaller diameter can be used duringassembly of the capacitor 200 shown in FIG. 4. Once chemical processingand other assembly is complete, however, the second anode lead 40 can betrimmed to approximately the same length as the first anode lead 30.Then, the second anode lead 40 can be attached to the upstanding portion42 of the anode termination 35 at notch 43 as shown in FIG. 4, while thefirst anode lead 30 can be attached to the upstanding portion 42 of theanode termination 35 at notch 47, as also shown in FIG. 47, such as bylaser welding or resistance welding. Such a configuration as discussedabove can reduce the ESR of the capacitor compared to when a singleanode lead is utilized and also enables for easier processing of thecapacitor element due to the smaller diameter second anode lead.

Another embodiment of the present disclosure includes the capacitorelement 300 and capacitor 400 of FIGS. 5-8. The capacitor element 300 ofFIGS. 5-7 has a porous anode body 33 having the same dimensions asdiscussed above in reference to the capacitor element 100 of FIGS. 1-3.

Further, as shown in FIG. 5, the first anode lead 30 can have a firstportion 30 a that extends from a surface of the porous anode body 33,such as front surface 36, and a second portion 30 b that is positionedwithin the anode body 33. The thickness/diameter of the first anode lead30 may vary depending on the overall size of the anode body 33. In anyevent, the larger the thickness/diameter D1 (see FIG. 6), the larger thenumber of points of contact between the porous anode body 33 and theanode lead 30 along embedded second portion 30 b, which results in alower ESR and improved electrical capabilities of the capacitor.

As shown in FIGS. 5-7, the first anode lead 30 extends from the frontsurface 36 of the porous anode body 33; however, it should be understoodthat the first anode lead 30 may also extend from any other surface ofthe porous anode body 33. Further, the first portion 30 a of the firstanode lead 30 that extends from a surface of the porous anode body 33can have a thickness D1 (see FIG. 6 showing the front view of thecapacitor element 100), which, as mentioned above, also refers to thethickness of the second portion 30 b of the first anode lead 30 that isembedded within the porous anode body 33.

Additionally, the capacitor element 300 of FIG. 5 also includes a secondanode lead 40 as part of its anode lead assembly 50. As shown, thesecond anode lead 40 can have a thickness/diameter D2 (see FIG. 6) thatis smaller than the thickness/diameter of D1. In the particularcapacitor element 300 of FIG. 5, the second anode lead 40 can beconnected directly to end 34 of the second portion 30 a of the firstanode lead 30 and can extend therefrom in a longitudinal (z) directionof the porous anode body via any suitable method as discussed in detailabove.

Initially, the length L1 of the first portion 30 a of the first anodelead 30 is shorter than the length L2 of the second anode lead 40, andthe second anode lead 40 is used as a carrier wire during chemicalprocessing such as anodization and cathode buildup, as well as duringany other phases of the assembly of the capacitor. The various rangesfor the lengths of each of the anode leads are discussed in detailabove, and generally the length L1 of the first portion 30 a of thefirst anode lead 30 is less than the length L2 of the second anode lead40 to minimize the internal resistance attributed to the first anodelead 30, which, in turn, reduces the ESR. Further, the amount ofmaterial required for the first anode lead 30 is reduced, which is morecost efficient. Meanwhile, the second anode lead 40 has a length L2 thatis longer so that the second anode lead 40 having a smaller diameter canbe used during assembly of the capacitor 400 shown in FIG. 8 to simplifythe process. After processing, however, the length L2 of the secondanode lead 40 can be trimmed to any suitable length and then attached tothe upstanding portion 42 of the anode termination 35 at notch 43 asshown in FIG. 8. Because the second anode lead 40 has a smaller diameterD2 than the diameter D1 of the first portion 30 a of the first anodelead 30, the anode termination 35 can be more easily and efficientlyconnected to the anode lead assembly 50.

Yet another embodiment of the present disclosure includes the capacitorelement 300 and capacitor 500 of FIGS. 9-11. The capacitor element 500of FIGS. 9-11 has a porous anode body 33 having the same dimensions asdiscussed above in reference to the capacitor element 100 of FIGS. 1-3.However, in the embodiments of FIGS. 9-11, the first anode lead andsecond anode lead are formed from different materials, while this is notrequired in the embodiments of FIGS. 1-8.

Further, as shown in FIG. 9, the first anode lead 30 can have a firstportion 30 a that extends from a surface of the porous anode body 33,such as front surface 36, and a second portion 30 b that is positionedwithin the anode body 33. The thickness/diameter of the first anode lead30 may vary depending on the overall size of the anode body 33. In anyevent, the larger the thickness/diameter D1 (see FIG. 9), the larger thenumber of points of contact between the porous anode body 33 and theanode lead 30 along embedded second portion 30 b, which results in alower ESR and improved electrical capabilities of the capacitor.

As shown in FIGS. 9-11, the first anode lead 30 extends from the frontsurface 36 of the porous anode body 33; however, it should be understoodthat the first anode lead 30 may also extend from any other surface ofthe porous anode body 33. Further, the first portion 30 a of the firstanode lead 30 that extends from a surface of the porous anode body 33can have a thickness D1 (see FIG. 10 showing the front view of thecapacitor element 500), which, as mentioned above, also refers to thethickness of the second portion 30 b of the first anode lead 30 that isembedded within the porous anode body 33.

Additionally, the capacitor element 500 of FIG. 9 also includes a secondanode lead 40 as part of its anode lead assembly 50. As shown, thesecond anode lead 40 can have a thickness/diameter D2 (see FIG. 10) thatis the same as the thickness/diameter of D1. In the particular capacitorelement 500 of FIG. 9, the second anode lead 40 can be connecteddirectly to end 34 of the second portion 30 a of the first anode lead 30and can extend therefrom in a longitudinal (z) direction of the porousanode body via any suitable method as discussed in detail above. Itshould be understood, however, that the second anode lead 40 can have athickness/diameter that is larger than the thickness/diameter of thefirst anode lead (not shown).

Initially, the length L1 of the first portion 30 a of the first anodelead 30 is shorter than the length L2 of the second anode lead 40, andthe second anode lead 40 is used as a carrier wire during chemicalprocessing such as anodization and cathode buildup, as well as duringany other phases of the assembly of the capacitor. The various rangesfor the lengths of each of the anode leads are discussed in detailabove, and generally the length L1 of the first portion 30 a of thefirst anode lead 30 is less than the length L2 of the second anode lead40 to minimize the internal resistance attributed to the first anodelead 30, which, in turn, reduces the ESR. Further, the amount ofmaterial required for the first anode lead 30 is reduced, which is morecost efficient. Meanwhile, the second anode lead 40 has a length L2 thatis longer so that the second anode lead 40 having a smaller diameter canbe used during assembly of the capacitor 500.

As a result of the present disclosure, a capacitor may be formed thatexhibits excellent electrical properties as determined by the testprocedures described below. For example, the capacitor of the presentinvention can exhibit an ultralow ESR, such as about 300 milliohms (mΩ)or less, in some embodiments about 100 mΩ or less, in some embodimentsfrom about 0.01 mΩ to about 50 mΩ, and in some embodiments, from about0.1 mΩ to about 20 mΩ, determined at a frequency of 100 kHz and atemperature of 23° C.±2° C. In addition, the leakage current, whichgenerally refers to the current flowing from one conductor to anadjacent conductor through an insulator, can be maintained at relativelylow levels. For example, the numerical value of the normalized leakagecurrent of a capacitor of the present invention is, in some embodiments,less than about 0.1 μA/μF*V, in some embodiments less than about 0.01μA/μF*V, and in some embodiments, less than about 0.001 μA/μF*V, whereinμA is microamps and uF*V is the product of the capacitance and the ratedvoltage.

Test Procedures Equivalent Series Resistance (“ESR”)

ESR generally refers to the extent that the capacitor acts like aresistor when charging and discharging in an electronic circuit and isusually expressed as a resistance in series with the capacitor. ESR istypically measured using a Keithley 3330 Precision LCZ meter with KelvinLeads 2.2 volt DC bias and a 0.5 volt peak to peak sinusoidal signal, atan operating frequency of 100 kHz and temperature of 23° C.±2° C.

Capacitance (“Cap”)

The capacitance was measured using a Keithley 3330 Precision LCZ meterwith Kelvin Leads with 2.2 volt DC bias and a 0.5 volt peak to peaksinusoidal signal. The operating frequency was 120 Hz and thetemperature was 23° C.±2° C.

Leakage Current

Leakage current (“DCL”) was measured using a leakage test set thatmeasures leakage current at a temperature of 23° C.±2° C. and at therated voltage after a minimum of 30 seconds.

Laser Weld

The laser weld was done using a Trumpf Nd:YaG HAAS laser (emitting nearIR light at wavelength around 1,064 nanometers). The energy to weldgenerally refers to the amount of laser energy required to bond theanode lead to the anode termination/lead frame. The energy to weld issettled in Joules.

EXAMPLE 1

70,000 μFV/g tantalum powder was pressed into pellets to form a porousbody having a length of 4.15 mm, a width of 3.60 mm, and a thickness of0.95 mm. The tantalum powder was charged into the hopper of a tantalumdevice automatic molding machine and automatically molded together witha first tantalum wire having a diameter of 0.50 mm and pressed to adensity of 5.3 g/cm³ to manufacture a porous body. 70% of the overalllength of the anode lead was embedded in the porous anode body. Thepenetration of wire in the porous was 70% of the anode length. Thismolded body was left standing under reduced pressure at 1400° C. toobtain a sintered body.

A second tantalum wire having a diameter of 0.24 mm tantalum wire wasthen welded together by a resistance welding process with the end of theportion of the first, 0.50 mm diameter wire extending from the body.Thereafter, the second, 0.24 mm diameter tantalum wire was welded to anauxiliary stainless steel strip.

The tantalum anode was anodized at 13.1 V in a liquid electrolyte of0.1% phosphoric acid to make capacitors with 330 μF at 120 Hz. Aconductive polymer coating was then formed by dipping the anode into abutanol solution of iron (III) toluenesulfonate (Clevios™ C, H. C.Starck) for 5 minutes and consequently into 3,4-ethylenedioxythiophene(Clevios™ M, H. C. Starck) for 1 minute. After 45 minutes ofpolymerization, a thin layer of poly(3,4-ethylenedioxythiophene) wasformed on the surface of the dielectric. The anode was washed inmethanol to remove reaction by-products, anodized in a liquidelectrolyte, and washed again in methanol. This process was repeated 6times. Thereafter, the part was dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content of 2% andviscosity of 20 mPa·s (Clevios™ K, H. C. Starck). Upon coating, the partwas dried at 125° C. for 20 minutes. This process was not repeated.Thereafter, the part was dipped into a dispersedpoly(3,4-ethylenedioxythiophene) having a solids content of 2% and aviscosity of 160 mPa·s (Clevios™ K, H. C. Starck). Upon coating, thepart was dried at 125° C. for 20 minutes. This process was repeated 8times. The part was then dipped into a graphite dispersion and dried.Finally, the part was dipped into a silver dispersion and dried. Thefinished part was completed by conventional assembly technology and thenmeasured. A copper-based leadframe was used for finishing of theassembly process. Once the capacitor element was attached via a laserwelding process to bond the anode lead wire to the anode termination,the length L2 of the second anode lead 40 was set to 0.80 mm. Next, theleadframe was enclosed with an encapsulating epoxy resin. Multiple parts(1500) of 330 μF/6.3V capacitors were made in this manner.

EXAMPLE 2

Capacitors were formed in the manner described in Example 1, except thatthe length L2 of the second anode lead 40 was set to 0.1 mm. Multipleparts (1500) were made in this manner.

COMPARATIVE EXAMPLE 3

Capacitors were formed in the manner described in Example 1, except thatonly a single lead wire with a diameter of 0.24 mm was utilized.Multiple parts (3000) were made in this manner.

COMPARATIVE EXAMPLE 4

Capacitors were formed in the manner described in Example 1, except thatonly a single lead wire with diameter of 0.50 mm was utilized. Multipleparts (3000) were made in this manner.

Table 1 below summarizes the characteristics of examples 1-4 discussedabove, including the tantalum wire diameters, the laser weld setting,the median DCL, the median capacitance, and the median ESR of thefinished capacitors.

TABLE 1 Ta wire Ta wire diameter diameter Laser (anode (anode Weld lead40) lead 30) Energy DCL CAP ESR [mm] [mm] [J] [μA] [μF] [mΩ] Example 10.24 0.50 9.5 11.2 298.0 22.1 Example 2 0.24 0.50 14.0 34.1 299.2 19.6Comparative — 0.24 9.0 9.7 308.0 30.4 Example 3 Comparative — 0.50 36.0N/A N/A N/A Example 4

As shown in Table 1, the benefit of using a thin wire/thick wire anodelead assembly is for better (lower) ESR values when compared with thecomparative examples using only a single lead wire. Electrical data forcomparative examples 4 is not available because the laser weldingprocess could not be completed.

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

What is claimed is:
 1. A solid electrolytic capacitor that comprises acapacitor element, the capacitor element comprising: a sintered, porousanode body; a first anode lead, wherein a first portion of the firstanode lead is embedded within the porous anode body and a second portionof the first anode lead extends from a surface of the porous anode bodyin a longitudinal direction; a second anode lead, wherein the secondanode lead is positioned external to the porous anode body, furtherwherein the second anode lead is not embedded within the porous anodebody; a dielectric layer overlying the sintered porous anode body; and acathode overlying the dielectric layer that includes a solidelectrolyte.
 2. The solid electrolytic capacitor of claim 1, wherein thesecond anode lead has a thickness that is smaller than the thickness ofthe first anode lead.
 3. The solid electrolytic capacitor of claim 2,wherein the thickness of the second anode lead is from about 10% toabout 90% of the thickness of the first anode lead.
 4. The solidelectrolytic capacitor of claim 2, wherein the thickness of the firstanode lead is from about 100 micrometers to about 2000 micrometers. 5.The solid electrolytic capacitor of claim 2, wherein the thickness ofthe second anode lead is from 10 micrometers to about 1800 micrometers.6. The solid electrolytic capacitor of claim 2, wherein the first anodelead and the second anode lead are the same material.
 7. The solidelectrolytic capacitor of claim 2, wherein the first anode lead and thesecond anode lead are different materials.
 8. The solid electrolyticcapacitor of claim 1, wherein the first anode lead is a differentmaterial than the second anode lead, further wherein the second anodelead has a thickness that is the same as or larger than the thickness ofthe first anode lead.
 9. The solid electrolytic capacitor of claim 1,wherein the second anode lead is connected to the surface of the porousanode body such that the second anode lead is adjacent to and in contactwith the second portion of the first anode lead.
 10. The solidelectrolytic capacitor of claim 9, wherein the second anode lead isconnected to the surface of the porous anode body by resistance welding.11. The solid electrolytic capacitor of claim 9, wherein the secondanode lead is connected to the surface of the porous anode body by laserwelding.
 12. The solid electrolytic capacitor of claim 1, wherein thesecond anode lead is connected to the second portion of the first anodelead.
 13. The solid electrolytic capacitor of claim 12, wherein thesecond anode lead extends beyond the second portion of the first anodelead in a longitudinal direction.
 14. The solid electrolytic capacitorof claim 12, wherein the second anode lead is connected to the secondportion of the first anode lead by resistance welding.
 15. The solidelectrolytic capacitor of claim 12, wherein the second anode lead isconnected to the second portion of the first anode lead by laserwelding.
 16. The solid electrolytic capacitor of claim 1, wherein theanode body is formed from a powder having a specific charge of fromabout 10,000 ρF*V/g to about 600,000 ρF*V/g, wherein the powdercomprises a valve metal such as tantalum, niobium, aluminum, hafnium,titanium, an electrically conductive oxide thereof, or an electricallyconductive nitride thereof.
 17. The solid electrolytic capacitor ofclaim 1, further comprising an anode termination that is electricallyconnected to the second anode lead and a cathode termination that iselectrically connected to the cathode.
 18. A method for forming a solidelectrolytic capacitor comprising a sintered, porous anode body, themethod comprising: positioning a first portion of a first anode leadwithin a powder formed from a valve metal composition such that a secondportion of the first anode lead extends from a surface of the anode bodyin a longitudinal direction; compacting the powder around the firstportion of the first anode lead; sintering the compacted powder and thefirst portion of the first anode lead to form the porous anode body;positioning a second anode lead external to the porous anode body; andwelding the second anode lead to an anode termination to form anelectrical connection between the second anode lead and the anodetermination.
 19. The method of claim 18, wherein the second anode leadis connected to the surface of the porous anode body such that thesecond anode lead is adjacent to and in contact with the second portionof the first anode lead, wherein the second portion of the first anodelead is also welded to the anode termination.
 20. The method of claim19, wherein the second anode lead is welded to the surface of the porousanode body.
 21. The method of claim 18, wherein the second anode lead isconnected to the second portion of the first anode lead.
 22. The methodof claim 21, wherein the second anode lead is extends beyond the secondportion of the first anode lead in a longitudinal direction.
 23. Themethod of claim 21, wherein the second anode lead is welded to thesecond portion of the first anode lead.
 24. The method of claim 18,further comprising trimming the second anode lead.
 25. The method ofclaim 18, further comprising: anodically oxidizing the sintered, porousanode body to form a dielectric layer; and applying a solid electrolyteto the anodically oxidized sintered anode body to form a cathode. 26.The method of claim 25, further comprising: forming an electricalconnection between the cathode and a cathode termination; andencapsulating the capacitor with a molding material such that at least apart of the anode termination and a part of the cathode terminationremain exposed.
 27. The method of claim 18, wherein the second anodelead has a thickness that is smaller than the thickness of the firstanode lead.
 28. The method of claim 27, wherein the first anode lead andthe second anode lead are the same material.
 29. The method of claim 27,wherein the first anode lead and the second anode lead are differentmaterials.
 30. The method of claim 18, wherein the first anode lead is adifferent material than the second anode lead, further wherein thesecond anode lead has a thickness that is the same as or larger than thethickness of the first anode lead.